1. Field of Art
The present invention generally relates to the field of integrated semiconductor circuits, and more specifically, to high-speed integrated semiconductor circuits for interfacing with digital video or audio.
2. Description of the Related Art
DisplayPort is an industrial standard of digital interface between two or more devices. Commonly, a DisplayPort interface controls transfer of video and/or audio from a source device, such as a computer, a digital video disk (DVD) player or a digital video recorder (DVR), to a sink device, such as a television, a home theater system or a computer monitor. DisplayPort uses two channels, a Main Link and an Auxiliary Channel (AUX-CH) for communication between source device and sink device. The Main Link serially transmits video, audio and other secondary data at rates of 1.62 Gigabits per second (Gbps) or 2.7 Gbps while the AUX-CH carries management and device control data for establishment or configuration of the Main Link at a rate of 1 Megabit per second (Mbps). Transmission of data through the AUX-CH is initiated by the source device allowing the source device to modify Main Link characteristics, although the sink device may prompt modification of the Main Link by sending an interrupt request (IRQ) to the source device via the AUX-CH.
A common function for the AUX-CH is handshaking to train the Main Link between source device and sink device. Depending on the distance between the source device and the sink device, the source device and sink device use different parameter sets to optimize data transmission through the Main Link. Link training allows the source device and sink device to negotiate with each other to determine the optimal Main Link parameter settings for different transmission scenarios. For example, link training allows the source device and sink device to determine values for lane counter, link rate, transmission main link voltage swing, main link pre-emphasis to optimize transmission. For example, when the source device and sink device connected by a short length of DisplayPort cable, a high bit rate is used with minimum voltage swing and no pre-emphasis. Alternatively, when the source device and sink device are connected by a long length of DisplayPort cable, a low bit rate is used with higher voltage swing and pre-emphasis values. However, when the source device and sink device are connected by a long length of DisplayPort cable, data transmitted along the AUX-CH is attenuated, weakening the data received by the sink device.